|Turned up to eleven: Fair and Balanced|
Thursday, April 04, 2002
Charles Murtaugh has a bunch of interesting biomedical science articles on his site, and one on HIV/AIDS in Africa in particular that I would like to elaborate on. Here is a quote;
Lowe poses, but doesn't answer, the question of why sub-Saharan Africa has such endemic HIV infection. In the U.S., as Michael Fumento has extensively documented (see, I told you I usually agree with Fumento), HIV has still made few inroads into the heterosexual population, excepting IV drug users. It seems hard to imagine that there are a lot more gays or IV drug users in Africa, so there must be some other reason explaining the rapid spread of HIV there.
I am inclined to disagree with Charles here, although social factors surely play a role, and may turn out to be the most important in the spread of HIV in Africa, there is an additional pathogenesis difference that has been completely unreported, to my knowledge, in the press. The details are complicated, and without a grounding in immunology, difficult to understand, but I will refer to my previous post on immunity(scroll down to March 20) for some of that. The adaptive immune system (T cells, B cells, located throughout the body, concentrated in lymph nodes and the spleen) is responsible, as I mentioned in that previous post, for response to specific pathogens. In particular, there is a complex system that determines, for a given infection, whether the body will choose to use humoral immunity (primarily antibodies) to defend itself, or cellular immunity (primarily cells which kill the invading cells, or host cells harboring a virus or intracellular bacterium). Infection with a virus, such as HIV, ought to stimulate the cellular immunity, which creates a specific type of T-cell called a Cytotoxic T-lymphocyte (CTL, often called a killer T-cell), which seeks out infected cells in the body, and kills them (this is in itself a very interesting process, but not our topic). Other infections, such as parasitic worm infections, cause induction of antibody responses primarily (this is sometimes called a Th2 response, because a type of T-cell called a T-helper 2 is formed that produces chemical signals that cause antibody production to be preferred to cytotoxic cell production). As always, there is some overlap in these systems, but the basic paradigm holds.
So, what does this have to do with HIV infection in Africa? In the developing world, parasitic infections are widespread. Among the most common are helminthic infections, and their staggering prevalence is described here. A lot of these infections are concentrated in sub-Saharan Africa (in particular, schistosomiasis, and trypanosomiasis(not a worm, but a parasite) are concentrated in these regions, but almost 1/2 of the world's population is infected with parasitic worms). It is not entirely clear what these infections may do in the context of HIV infection, but it is well known that parasitic worm infections drastically alter the immune responses in their hosts, and several reviews have posited a connection between disease course and parasitic co-infection. It has been suggested several times, in reputable scientific studies, that helminthic infections significantly alter the course of HIV disease (here is a review article abstract which makes a related claim for HIV and TB). I will note that this is a bit of a controversial idea, and research in a murine AIDS model suggests that it might be more complicated. I won't get into the problems with murine disease models, but I will note that sometimes, the comparisons are inapposite. There is also a possibility that infection may be affected, since the infection process for HIV is related to the presence of specific cell markers on the exterior of T-cells and macrophages, and the prevalence of those markers is directly related to the immune systems' choices of humoral v. cellular immunity. This possibility is backed up by epidemiological data. Because so called CD-4+ T-cells are the helper cells responsible for the choice, and they happen to be the target (or, more correctly, one of the targets) of HIV, it is clear that these coinfections are deeply intertwined, but the mechanisms and overall impacts are less clear. In effect, it may be that the prevalent helminthic infections and other parasites are priming the population specifically for HIV infections, or they make the disease manifest more quickly (this is almost certainly true), or both (as I think most likely).
This explanation, of course, is not great news for social conservatives, who would like to believe that promiscuity or other societal factors are to blame, and therefore the solution lies there. It's also not great news for liberal activists, who would like to cure AIDS by handing out condoms or by ending poverty (that last bit would certainly help, although I think clean water is much more important. In effect, though, the primary responsibility for curbing or curing HIV/AIDS must be in the scientific community, and the research, both primary and drug and vaccine development, is of paramount importance. Of course, as a working scientist, that makes me happy, so perhaps I am not a totally unbiased observer either (this gets pretty complex, huh?)
Ted Barlow for pointing people here to hear (ha!) my thoughts on Lomborg's book. Two pieces of advice. 1) Go to Bjorn Lomborg's site. He has lots of info, including published critiques and his responses, which is very interesting, and hopefully will start a trend in popular science publishing; and 2) go back to Ted's site, because he has tons of good stuff there!!
Wednesday, April 03, 2002
Derek Lowe has some interesting insights into the future of medicine, with respect to costs, efficacy, and overall health. They are worth reading, as always. These are issues I have contemplated for some time, and I will post on them in the near future.
The Worldwatch Institute, a public policy advocacy group. Interestingly, this group is singularly unqualified to comment or analyze the state of the world, although that doesn't stop them. An excerpt from the bio of the director of research, Gary Gardner;
Mr. Gardner holds Master's degrees in Politics from Brandeis University, and in Public Administration from the Monterey Institute of International Studies, and a Bachelor's degree from Santa Clara University.
Leaving aside that their director of research doesn't hold a Ph.D., he doesn't even have a degree in Science!!! How is he qualified to direct environmental science research? This is an advocacy group, pure and simple. It is not clear that there is anyone at this institute with even a degree in environmental science, let alone a Ph.D. Now, I may be a bit of a snob about this, but how exactly are you supposed to determine the state of the environment when no one on your staff has the training to do it?
In sum, returning to the subject at hand, I don't know that attacking the "Worldwatch Institute" is very useful, as they don't seem particularly well suited to environmental analysis, and don't appear to have much influence. As an example, in E.O. Wilson's piece in the same magazine, many mainstream environmental groups are mentioned, but this one is not. Draw your own conclusions, I suppose, but it seems a waste of time to argue that a hard-core environmental advocacy group is stretching the truth. Still, it could be argued that this is useful. What disturbed me most in reading Lomborg's book, however, was how often he failed to provide citations for his own assertions that the environmentalists were wrong.
An example, referring to Dr. Pimentel's assertion that environmental changes have caused increased infectious disease rates;
Finally, we get to Pimentel's central claim that infections have increased and will continue to increase. Both of these are false. The reason Pimentel tells use all these (sometimes incorrect) stories and gives examples of many and new diseases is to make us feel that disease frequency must be increasing....(it goes on for a while)
It is not true that death from disease will increase
This is a classic strawman argument. It conflates two distinctly different notions, that of infection, and that of death from disease. The article uses the tuberculosis incidence as evidence of environmentalist wrongheadedness, noting that Dr. Pimentel made a prediction of increases in TB deaths based on a small sample of the data, rather than the long term trend of reduced death, and the current predictions of steady states of TB deaths. However, both are ignoring the central motif of tuberculosis, which is that a staggering number of people are infected with Mycobacterium tuberculosis, and the slowly progressing disease will kill the vast majority of them, because the required antibiotics are scarce and expensive, and most of these people are terribly poor. In point of fact, the rate of deaths from TB is probably going to fluctuate wildly around a steady state that reflects the vast majority of people who don't have access to preventive medicine. In general, however, this is not particularly reflective of the real state of the world in terms of infectious disease.
In fact, I think TB is not a very good example of a disease that is relevant to discussion of environmental issues, because it is much more a disease of poverty, with no known habitat restriction (unlike malarial parasites, for example, pools of standing water do not serve as vector reservoirs for tuberculosis bacilli, which are essentially only human pathogens). The course of anti-TB antibiotics is also very long (~1 year), because the organism is very tough to get rid of. There are any number of diseases that are better examples of direct environmental causes of disease incidence. Just a list off the top of my head; cholera, dysentery, E.coli diarrheal disease (all caused by lack of clean drinking water), yellow fever, malaria, dozens of hemorrhagic virus diseases that have followed the trajectory of their normal host animals, usually rodents or insects, into encroaching human populations. For a great insight into this, read The Coming Plague by Laurie Garrett.
What is most interesting about this excerpt of Lomborg's book, however, is the overall strawman that he (and anti-environmentalists, who I do not think he represents) is trying to erect, of an overall environmental establishment that is hostile to good news. In fact, real environmental scientists are proud of their accomplishments, particularly with respect to saving what they view as precious biological diversity. If you want an accurate picture of the real state of the environment, compare Wilson's essay in the same issue of Skeptic with Lomborg's. To summarize, Lomborg is busy trying to discredit fringe environmental advocacy groups, while Wilson is working with mainstream groups like the World Wildlife Foundation and the Nature Conservancy to create economic incentives for Third World countries to create rain forest preserves (for example). In the long run, which do you, gentle reader, think will be more successful?
Lomborg, and his book, The Skeptical Environmentalist. While I have not read the book, I have read a chapter that was published, in its entirety with figures and footnotes, in Skeptic Magazine. My presumption is that Dr. Lomborg was allowed to choose the chapter to be included, which was followed by a rebuttal by a scientist (Dr. Dave Pimentel of Cornell) who was criticized in that chapter. My next post will describe my impressions of both pieces, as well as an additional excerpt from E.O. Wilson's new book, The Future of Life.
First, some caveats; I am not an environmentalist, but I am a concerned observer. It seems to me, from my coursework and outside reading on the subject, that we are just beginning to get a firm scientific grip on how human activity affects the world around us, and the various complex feedback loops that are involved. Because the mathematics of feedback loops containing several interacting parts (in the case of an ecosystem, several can mean thousands!) are very difficult, and because biology in general has been dominated by an exploratory rather than an analytical approach(a fancy way to say that biologists don't do enough math), predictions of the environmental future are notoriously bad. Nevertheless, I think that our future depends on understanding these phenomena, and how they will affect our lives, and those of our children (won't somebody please think of the children??). Let's be clear; the Earth will survive our actions just fine. What will happen to us, however, is much less clear. This is what we should focus on, and how the debate must be framed.
Monday, April 01, 2002
Lagniappe has a great essay on paying attention to the little anomalies in scientific research, and the dichotomy between getting things done and figuring things out. Worth reading, especially for the working scientist.